1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic process or an electrostatic recording process, and more particularly to an image forming apparatus such as a copying machine, a printer, a facsimile machine and a composite machine including a plurality of functions of the above-mentioned apparatus.
2. Description of Related Art
In an image forming apparatus for forming a color image by superposing a plurality of toner images each having different colors, for example as shown in FIG. 5, an image forming apparatus 70 using an intermediate transfer member 54 has been proposed conventionally with an object of obtaining a color image having no color shifts.
In the image forming apparatus 70, charging means 51, exposure means 52 and developing means 53 are disposed around an electrophotographic photosensitive member 50 as an image bearing member, and a developer image (toner image) is formed by performing a charging process, an exposure process and a developing process of each color sequentially on the basis of image information analyzed to each color. Then, the formed developer images are superposed on the intermediate transfer member 54, and a color image is formed on a recording material P such as paper, which is conveyed with conveyance rollers 55.
Hereupon, the developing means 53 for performing the developing process is composed of a rotation developing apparatus 53a and a fixed developing apparatus 53b. The rotation developing apparatus 53a adopts a rotation switching system and is mounted with a yellow developing device 53Y, a magenta developing device 53M and a cyan developing device 53C, which contain three kinds of color toners of yellow, magenta and cyan, respectively, as developers. The fixed developing apparatus 53b includes a black developing device 53B adopting a fixed system and containing a black toner as a developer.
The respective developing devices 53Y, 53M, 53C and 53B includes developing containers 532y, 532m, 532c and 532k for containing developers, developer bearing members 531y, 531m, 531c and 531k for conveying developers from the respective developing containers 532y–532k to the electrophotographic photosensitive member 50, and developer layer thickness regulating members (not shown) for regulating the quantities of the developers conveyed by the developer bearing members 531y–531k. Developing sleeves each formed to be a cylindrical sleeve rotating with a developer put on its peripheral surface are generally used as the developer bearing members 531y–531k. Developing blades formed in blades severally opposed to the developer bearing surfaces of the developer sleeves 531y–531k with a predetermined distance between each of the blades and each of the developer bearing surfaces are generally used as the developer layer thickness regulating members (layer thickness regulating members).
The use of the rotation developing apparatus 53a adopting the rotation switching system removes the necessity of consideration of the shapes of the developing devices according to respective dispositions, which consideration is required in case of disposing the developing devices 53Y, 53M and 53C of respective colors as individual bodies around the electrophotographic photosensitive member 50. Moreover, the capability of the color toner developing devices 53Y, 53M and 53C to be rotated and switched brings about an advantage enabling the size reduction of the rotation developing apparatus 53a. Moreover, because the number of the devices disposed around the electrophotographic photosensitive member 50 can be decreased, the image forming apparatus 70 has an advantage that the fixed developing apparatus 53b can increase its capacity of a black toner, which is generally consumed much.
Generally, four kinds of developing methods can be adopted as a developing method of the above-mentioned developing means 53 in case of using a non-magnetic toner as a developer. One of the developing methods is a one-component noncontact developing method for performing development with a toner being noncontact with a photosensitive drum being an electrophotographic photosensitive member, which toner is conveyed to the photosensitive drum by the rotation of a developing sleeve after the toner has been coated on the developing sleeve with a blade or the like. Another developing method is a one-component contact developing method for performing development with the toner being contact with the photosensitive drum. A further method is a two-component noncontact developing method for performing development with a developer being noncontact with a photosensitive drum, which developer to be used is a two-component developer made of mixing a non-magnetic toner and a magnetic carrier and is conveyed to the photosensitive drum with being borne on a developing sleeve by a magnetic force. A still further developing method is a two-component contact developing method for performing development with the developer being contacted with the photosensitive drum.
Among the above-mentioned four developing method, the two-component contact developing method using the developer made of mixing the toner and the magnetic carrier, i.e. the two-component developer, for performing the development with the developer being contact with the photosensitive drum has a high resolution and can easily obtain a half tone. Consequently, the two-component contact developing method are frequently used for an image forming apparatus such as a full color copying machine, which is demanded to have a high image quality.
Conventionally known carriers can be used as the carrier constituting the two-component developer to be used for the two-component contact developing method. The usable carriers are, for example, a resin carrier formed by dispersing magnetite as a magnetic material in a resin and by dispersing carbon black into the resin for making the resin conductive and for adjusting the resistance thereof, a carrier made by performing of the oxidization-reduction processing of the surface of a simple substance of magnetite such as ferrite for adjusting the resistance thereof, a carrier made by coating the surface of a simple substance of magnetite such as ferrite with a resin for adjusting the resistance thereof, and the like. The manufacturing methods of these magnetic carriers are not especially limited.
Moreover, a one-component jumping developing method using a one-component magnetic toner as a developer for performing development in a noncontact state by applying an alternating electric field to the developer has been generalized already as one of the most superior developing methods. The one-component jumping developing method has great advantages to obviate the control of the mixture ratio between a toner and a carrier in a developer, which control is necessary for the two-component developing methods, the absence of the problem of the deterioration of the carrier, and the capability of obtaining stable images for a long period.
Moreover, because the color of the magnetic material to be compounded into the one-component magnetic toner is generally black in the one-component jumping developing method, the method can be applied to the case of forming a black image using a black toner very suitably.
Moreover, at the time of charging the magnetic toner in the one-component jumping developing method, for example, the abutting of an elastic blade as a layer thickness regulating member against a metal rigid body sleeve being a developer bearing member, or the abutting of a metal blade as a layer thickness regulating member against an elastic sleeve as a developer bearing member brings about a good toner frictional electrification property and a uniform toner thin layer. Consequently, it is known that a high quality image output can be obtained with a simple configuration.
However, the adoption of such a developing blade method using the layer regulating members such as the elastic blade and the metal blade easily causes the deterioration of the toner owing to the stress upon the passage of the developing blade and the generation of much frictional heat, and consequently prevents the compatibility of the high image quality property of a toner image formed by the developing method and the lengthening of the life as the developing means.
Accordingly, for making the best use of the above-mentioned merit of the one-component jumping developing method enabling the stable acquisition of images for a long period, a toner regulating method changing the conventional developing blade system to use a magnetic blade or the like in a noncontact state with a developing sleeve has been proposed.
However, it is difficult to apply the proposed toner regulating method to a case using color toners such as a magenta toner, a cyan toner and a yellow toner at present.
Consequently, the following developing method (jumping and brush developing method) is more suitable for the development of the color toners of magenta, cyan and yellow and the like. In the developing method, a two-component developer formed by mixing a non-magnetic toner and a carrier is used, and a magnetic brush of the developer thin layer is formed on a developing sleeve to contact the magnetic brush with a photosensitive drum, and then an alternating electric field is applied to the photosensitive drum to perform development.
Moreover, when a full color copying machine is also used as a black-and-white copying machine, the frequency of using a black developing apparatus is very high. Consequently, the use of a one-component jumping development method into a black station is especially advantageous.
Consequently, an image forming apparatus using two-component development using a non-magnetic toner for the development the color toners of magenta, cyan, yellow and the like and magnetic one-component jumping development for the development of a black toner is regarded as a preferable one.
Now, in recent years, the use of a sheet of recording paper printed with an image forming apparatus as a direct print manuscript has been begun to be performed as the quality of the printing of the image forming apparatus has become higher.
There is a process for producing a manuscript called as an art work (or a block copy) by applying a character or a figure which is wanted to be printed on a sheet of white thick paper as a material of the art work among the printing work processes performed in the above-mentioned printing method using the recording paper. Also in the case of printing an image printed with the image forming apparatus, a process of sticking a sheet of recording paper as a recording material on which an image is formed to an art work material having a size larger than that of the sheet of recording paper is provided.
FIG. 3 shows a general form of an art work 19. On the art work 19, marks for registration are put on the outside of a print region 18 to be an object of printing including an image forming region and an image non-forming region, namely an area to which a sheet of recording paper printed with an image forming apparatus is stuck, for the location of the art work 19 to a printing machine. Such marks for registration are called as registration marks (designated by reference marks M1), and also called as dragonflies (register marks) from their shapes. The marks M1 could also be referred to as “alignment marks.”
For example, for printing a double-spread page of the fourth sizes in A series, a sheet of recording paper P having the third size of the A series is used. Characters or figures are edited on the recording paper P, and the recording paper P is stuck in the print region 18 of an art work (block copy) material 17 while the position of the recording paper P is adjusted to the registration marks M1 formed on the thick paper having the size larger than that of the sheet of the recording paper P as the art work material 17 in order that the recording paper P, on which characters and figures are formed, may fall in the print region 18. Thus, the art work 19 is produced.
That is, the recording paper P is stuck on the art work material 17 in order that the recording paper P may fall in the inside of the registration marks M1 formed at four corners and both the sides of the central part of the print region 18.
Hereupon, if it is possible to use a sheet of art work material recording paper 17a having the same size as that of the art work material 17, and to apply the printing, being an image formed by an image forming apparatus on the usual recording paper P to be stuck in the print region 18, within the third size of A series to the art work material recording paper 17a, and further to print the registration marks M1 on the recording paper 17a at the same positions as those on the art work material 17, then the recording paper 17a itself can be used as the art work 19, and the art work 19 can be directly produced with the image forming apparatus. In this case, it is unnecessary to stick the recording paper P on the art work material 17, and consequently, the processes for printing can be reduced.
However, the sheet of the art work material recording paper 17a to be used for the production of the art work 19 has a size larger than that of the sheet of the standard recording paper P against an image to be formed, and there are a case where the positions at which the registration marks M1 are printed are positions corresponding to margin portions of the standard recording paper P. Consequently, it is apprehended that the image forming apparatus becomes large in size.